Method for fabricating multilevel interconnection structure for semiconductor devices

ABSTRACT

The present invention provides a novel interconnection structure which comprises an insulation layer having a contact hole which extends in a first vertical direction, a contact layer residing within the contact hole and being made of a first conductive material which has a first electromigration resistance, and an interconnection layer extending within the insulation layer. The interconnection layer has one end portion which is in contact with one end of the contact layer. The interconnection layer is made of a second conductive material having a second electromigration resistance which is smaller than the first electromigration resistance. The interconnection layer has a reservoir portion which is made of the second conductive material. The reservoir portion extends within the insulation layer and extends from the one end portion of the interconnection layer in a second vertical direction which is opposite to the first vertical direction.

This application is a division of application Ser. No. 08/591,301, filedJan. 25, 1996 now U.S. Pat. No. 5,793,113.

BACKGROUND OF THE INVENTION

The present invention relates to a multilevel interconnection structurefor a semiconductor device and a method for forming the same.

One of the typical multilevel interconnections is illustrated in FIG. 1.Field oxide films 2 are selectively formed on a top surface of a siliconsubstrate 1 to define an active region of the substrate. A firstinter-layer insulator 3 with a first contact hole is formed on the fieldoxide film 2 and the active region. A titanium film 5 is formed on thefield oxide film 2 and on both a vertical side wall and a bottom of thefirst contact hole. A titanium nitride film 6 is formed on the titaniumfilm 5. A tungsten plug is selectively provided within the first contacthole. An aluminum film 9 is formed on the titanium nitride film 6. Atitanium nitride film 10 is formed on the aluminum film 9. A firstinterconnection layer 11 comprises the titanium film 5, the titaniumnitride film 67 the aluminum film 9 and the titanium nitride film 10. Asecond inter-layer insulator 41 with a second contact hole over thefirst interconnection layer 11 is formed on the first interconnectionlayer 11 and on the first inter-layer insulator 3. A titanium film 15 isformed on the second inter-layer insulator 41 and on both a verticalside wall and a bottom of the second contact hole. A titanium nitridefilm 16 is formed on the titanium film 15. A tungsten plug 17 isselectively provided within the first contact hole. An aluminum film 18is formed on the titanium nitride film 16. A titanium nitride film 19 isformed on the aluminum film 18. A second interconnection layer 20comprises the titanium film 15, the titanium nitride film 16, thealuminum film 18 and the titanium nitride film 19. A third inter-layerinsulator 42 is formed on the second interconnection layer 20 and on thesecond inter-layer insulator 41.

When electrical current flows through the aluminum interconnection,electromigration is likely to appear due to a small electromigrationresistance of aluminum. Aluminum atoms are likely to migrate along thecurrent of electrons. Electromigration may cause disconnection of theinterconnection. Refractory metals have relatively high electromigrationresistance. Refractory metal atoms decline to migrate, whilst aluminumatoms and non-refractory metal atoms incline to migrate. If electroncurrent flows from the refractory metal region to aluminum region, thenany void is likely to be formed in the aluminum region but in thevicinity of an interface to the refractory metal region. The formationof a void may lead to disconnection of the interconnection.

As illustrated in FIG. 2, a pair of low level interconnections 11 and11a are arranged at a pitch P which is relatively large, for example,1.6 micrometers. Another pair of high level interconnections 20 and 20aare connected to the low level interconnections via tungsten plugswithin contact holes. When currents of electrons flow through theinterconnections, tungsten atoms decline to migrate whilst aluminumatoms incline to migrate. For this reason, a hillock 44 and a void 43are likely to be formed as illustrated in FIG. 3. If the pitch P islarge, it is possible to provide pedestals 46 from which aluminum atomsare supplied to the void. However, the pitch has to be small when a highdensity integration is required. In this case, it is difficult toprovide any pedestals.

In the above circumstance, it had been required to develop quite novelmultilevel interconnection structures free from any problems with voidand hillock.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a novelinterconnection structure for a semiconductor device, which is free fromthe problems as described above.

It is another object of the present invention to provide a novel methodfor forming an interconnection structure for a semiconductor device,which is free from the problems as described above.

The present invention provides a novel interconnection structure whichcomprises an insulation layer having a contact hole which extends in afirst vertical direction, a contact layer residing within the contacthole and being made of a first conductive material which has a firstelectromigration resistance, and an interconnection layer extendingwithin the insulation layer. The interconnection layer has one endportion which is in contact with one end of the contact layer. Theinterconnection layer is made of a second conductive material having asecond electromigration resistance which is smaller than the firstelectromigration resistance. The interconnection layer has a reservoirportion which is made of the second conductive material. The reservoirportion extends within the insulation layer and extends from the one endportion of the interconnection layer in a second vertical directionwhich is opposite to the first vertical direction.

The present invention also provides another interconnection structurewhich comprises an insulation layer having a contact hole which extendsin a first vertical direction, a contact layer residing within thecontact hole and being made of a first conductive material which has afirst electromigration resistance, and an interconnection layerextending within the insulation layer. The interconnection layer has anintermediate portion which is in contact with one end of the contactlayer so that an electron current is divided at the intermediate portioninto two currents flowing on the interconnection layer in the oppositedirections. The interconnection layer is made of a second conductivematerial having a second electromigration resistance which is smallerthan the first electromigration resistance. The interconnection layerhas a reservoir portion which is made of the second conductive material.The reservoir portion extends within the insulation layer and extendsfrom the intermediate portion in a second vertical direction which isopposite to the first vertical direction.

The present invention also provides still another interconnectionstructure which comprises an insulation layer having a contact holewhich extends in a first vertical direction, a contact layer residingwithin the contact hole, the contact layer being made of a conductivematerial, and an interconnection layer being made of the same conductivematerial as the contact layer. The interconnection layer extends withinthe insulation layer in a horizontal direction. The interconnectionlayer has one end portion which is in contact with one end of thecontact layer so that an electron current flows on both the contactlayer and the interconnection layer. The electron current has a passagewhich is tuned at an almost right angle at a boundary between thecontact layer and the interconnection layer. The electron current has ahigher current density at the boundary than other portions of both theinterconnection layer and the contact layer. The interconnection layerhas a reservoir portion which is made of the same material as theinterconnection layer. The reservoir portion extends within theinsulation layer and extends from the end portion of the interconnectionlayer in a second vertical direction which is opposite to the firstvertical direction.

The present invention provides a further interconnection structure whichcomprises an insulation layer having a contact hole which extends in afirst vertical direction, a contact layer residing within the contacthole and being made of a conductive material, and an interconnectionlayer being made of the same conductive material as the contact layer.The interconnection layer extends within the insulation layer in ahorizontal direction. The interconnection layer has an intermediateportion which is in contact with one end of the contact layer so that anelectron current flows on both the contact layer and the interconnectionlayer. The electron current on the interconnection layer comprises twocurrents flowing in the opposite directions. The electron current has apassage which is turned at an almost right angle at a boundary betweenthe contact layer and the interconnection layer. The electron currentalso has a higher current density at the boundary than other portions ofboth the interconnection layer and the contact layer. Theinterconnection layer has a reservoir portion which is made of the samematerial as the interconnection layer. The reservoir portion extendswithin the insulation layer and extends from the intermediate portion ina second vertical direction which is opposite to the first verticaldirection.

The present invention provides a still further interconnection structurewhich comprises an insulation layer having a contact hole which extendsin a first vertical direction, a contact layer being provided within thecontact hole to fill up the contact hole, and an interconnection layer.The contact layer further comprises first, second and third contactfilms. The first contact film both extends on a vertical inner wall ofthe contact hole and fills up one end of the contact hole. The firstcontact film is made of a first conductive material having a firstelectromigration resistance. The second contact film extends on thefirst contact film and is made of a second conductive material having asecond electromigration resistance which is higher than the firstelectromigration resistance. The third contact film extends on thesecond contact film so flat laminations of the first, second and thirdcontact films fill up an entire part of the contact hole. The thirdcontact film is made of a third conductive material having a thirdelectromigration resistance which is substantially equal to or smallerthan the second electromigration resistance. The interconnection layerextends within the insulation layer and has end portion which isconnected with the one contact layer so that the interconnection layeris in contact with the first contact film. The interconnection layer ismade of the first conductive material.

The present invention provides yet a further interconnection structurewhich comprises an insulation layer having a contact hole which extendsin a first vertical direction, a contact layer being provided within thecontact hole to fill up the contact hole, and all interconnection layer.The contact layer further comprises first, second and third contactfilms. The first contact film both extends on a vertical inner wall ofthe contact hole and fills up one end of the contact hole. The firstcontact film is made of a first conductive material having a firstelectromigration resistance. The second contact film extends on thefirst contact film. The second contact film is made of a secondconductive material having a second electromigration resistance which ishigher than the first electromigration resistance. The third contactfilm extends on the second contact film so that laminations of thefirst, second and third contact films fill up all entire part of thecontact hole. The third contact film is made of a third conductivematerial having a third electromigration resistance which issubstantially equal to or smaller than the second electromigrationresistance. The interconnection layer extends within the insulationlayer. The interconnection layer has an intermediate portion which isconnected with the contact layer. The interconnection layer is incontact with the first contact film so that an electron current isdivided at the intermediate portion into two currents flowing on theinterconnection layer in the opposite directions. The interconnectionlayer is made of the first conductive material.

BRIEF DESCRIPTIONS OF THE DRAWINGS

Preferred embodiments of the present invention will be described indetail with reference to the accompanying drawings.

FIG. 1 is a fragmentary cross sectional elevation view illustrative ofthe conventional multilevel interconnection structure.

FIG. 2 is a fragmentary plane view illustrative of contact holes andinterconnection layers in the prior art.

FIG. 3 is a fragmentary cross sectional elevation view illustrative ofthe conventional multilevel interconnection layers having a large voidand a hillock, both of which are formed by electromigration.

FIGS. 4A through 4E are fragmentary cross sectional elevation viewsillustrative of novel multilevel interconnections and contact holeswithin inter-layer insulators in sequential steps involved in a novelfabrication method in a first embodiment according to the presentinvention.

FIGS. 5A through 5E are fragmentary cross sectional elevation viewsillustrative of novel multilevel interconnections and contact holeswithin inter-layer insulators in sequential steps involved in a novelfabrication method in a first embodiment according to the presentinvention.

FIG. 6 is a diagram illustrative of times until a half of sampleinterconnection layers comes into disconnection versus a volume ofaluminum film within a contact hole both in the prior art and in thepresent invention.

FIG. 7 is a fragmentary cross sectional elevation view illustrative ofnovel structure of multilevel interconnections and a contact hole in athird embodiment according to the present invention.

FIG. 8 is a fragmentary cross sectional elevation view illustrative ofnovel structure of multilevel interconnections and a contact hole in afourth embodiment according to the present invention.

FIG. 9 is a fragmentary cross sectional elevation view illustrative ofnovel structure of multilevel interconnections and a contact hole in afifth embodiment according to the present invention.

FIG. 10 is a fragmentary cross sectional elevation view illustrative ofnovel structure of multilevel interconnections and a contact hole in asixth embodiment according to the present invention.

FIG. 11 is a fragmentary cross sectional elevation view illustrative ofnovel structure is a fragmentary cross sectional elevation viewillustrative of novel structure of multilevel interconnections and acontact hole in a seventh embodiment according to the present invention.

FIG. 12 is a fragmentary cross sectional elevation view illustrative ofnovel structure of multilevel interconnections and a contact hole in aneighth embodiment according to the present invention.

FIG. 13 is a fragmentary cross sectional elevation view illustrative ofnovel structure of multilevel interconnections and a contact hole in aninth embodiment according to the present invention.

FIG. 14 is a fragmentary cross sectional elevation view illustrative ofnovel structure of multilevel interconnections and a contact hole in atenth embodiment according to the present invention.

FIG. 15 is a fragmentary cross sectional elevation view illustrative ofnovel structure of multilevel interconnections and a contact hole in aneleventh embodiment according to the present invention.

FIG. 16 is a fragmentary cross sectional elevation view illustrative ofnovel structure of multilevel interconnections and a contact hole in atwelfth embodiment according to the present invention.

FIG. 17 is a fragmentary cross sectional elevation view illustrative ofnovel structure of multilevel interconnections and a contact hole in athirteenth embodiment according to the present invention.

FIG. 18 is a fragmentary cross sectional elevation view illustrative ofnovel structure of multilevel interconnections and a contact hole in afourteenth embodiment according to the present invention.

DISCLOSURE OF THE INVENTION

The present invention provides a novel interconnection, structure whichcomprises an insulation layer having a contact hole which extends in afirst vertical direction, a contact layer residing within the contacthole and being made of a first conductive material which has a firstelectromigration resistances and an interconnection layer extendingwithin the insulation layer. The interconnection layer has one endportion which is in contact with one end of the contact layer. Theinterconnection layer is made of a second conductive material having asecond electromigration resistance which is smaller than the firstelectromigration resistance. The interconnection layer has a reservoirportion which is made of the second conductive material. The reservoirportion extends within the insulation layer and extends from the one endportion of the interconnection layer in a second vertical directionwhich is opposite to the first vertical direction.

If the first vertical direction is upward, then the second verticaldirection is downward. If the first vertical direction is downward, thenthe second vertical direction is upward.

It is available that the first conductive material is a refractorymetal. In this case, the refractory metal may, for example, be eithertungsten or titanium.

It is available that the first conductive material is titanium nitride.

Alternatively, it is available that the first conductive material is arefractory silicide.

It is available that the second conductive material is a non-refractorymetal which is not classified into refractory metals. In this case, thenon-refractory metal may, for example, be either Al, Cu or AlSiCu. Inthis case, it is optionally available to further provide a titaniumnitride film which coats an entire surface of the interconnection layerexcept for the reservoir portion, provided that the insulation layer ismade of silicon oxide, in order to physically isolate the non-refractorymetal from the insulation layer made of silicon oxide. In this case, itis optionally available to furthermore provide a titanium film which isinterposed between the titanium nitride film and the insulation layermade of silicon oxide.

It is available that the interconnection layer extends in a horizontaldirection so that the interconnection layer and the contact layer areconnected with each other at a right angle.

It is available that the contact layer may optionally comprise atitanium film extending at least on a vertical inner wall of the contacthole, a titanium nitride film extending on the titanium film, and atungsten film residing on the titanium nitride film so that laminationsof the titanium film, the titanium nitride film and the tungsten filmfill up an entire part of the contact hole. In this case, it isoptionally available that the titanium film not only extends on thevertical inner wall of the contact hole but also fills up the one end ofthe contact hole.

It is available that the reservoir portion has a horizontal section areawhich is nearly equal to a vertical section area of the interconnectionlayer.

It is available that the reservoir portion has a vertical length whichis substantially equal to or larger than a thickness of theinterconnection layer.

It is available to further provide an additional interconnection layerextending within the insulation layer, wherein the additionalinterconnection layer has one end portion which is in contact withanother end, which is opposite to the one end, of the contact layer, andwherein the additional interconnection layer is made of the secondconductive material. In this case, it is optionally available that theadditional interconnection layer has an additional reservoir portionwhich is made of the same material as the additional interconnectionlayer, wherein the additional reservoir portion extends within theinsulation layer and further extends from the one end portion of theadditional interconnection layer in the fist vertical direction. In thiscase, it is further optionally available that the additionalinterconnection layer has substantially the same structure and the samesection size as the interconnection layer. In this case, it isfurthermore optionally available that the additional reservoir portionhas substantially the same size as the reservoir portion.

The present invention also provides another interconnection structurewhich comprises an insulation layer having a contact hole which extendsin a first vertical direction, a contact layer residing within thecontact hole and being made of a first conductive material which has afirst electromigration resistance, and an interconnection layerextending within the insulation layer. The interconnection layer has anintermediate portion which is in contact with one end of the contactlayer so that an electron current is divided at the intermediate portioninto two currents flowing on the interconnection layer in the oppositedirections. The interconnection layer is made of a second conductivematerial having a second electromigration resistance which is smallerthan the first electromigration resistance. The interconnection layerhas a reservoir portion which is made of the second conductive material.The reservoir portion extends within the insulation layer and extendsfrom the intermediate portion in a second vertical direction which isopposite to the first vertical direction.

If the first vertical direction is upward, then the second verticaldirection is downward. If the first vertical direction is downward, thenthe second vertical direction is upward.

It is available that the first conductive material is a refractorymetal. In this case, the refractory metal may, for example, be eithertungsten or titanium.

It is available that the first conductive material is titanium nitride.

It is available that the first conductive material is a refractorysilicide.

It is available that the second conductive material is a non-refractorymetal which is not classified into refractory metals. In this case, themetal may, for example, be either Al, Cu or AlSiCu. In this case, it isavailable to further provide a titanium nitride film which coats anentire surface of the interconnection layer except for the reservoirportion, provided that the insulation layer is made of silicon oxide, inorder to physically isolate the non-refractory metal from the insulationlayer made of silicon oxide. It is available to further provide atitanium film which is interposed between the titanium nitride film andthe insulation layer made of silicon oxide.

It is available that the interconnection layer extends in a horizontaldirection so that the interconnection layer and the contact layer areconnected with each other at a right angle.

It is available that the contact layer comprises a titanium filmextending at least on a vertical inner wall of the contact hole, atitanium nitride film extending on the titanium film, and a tungstenfilm residing on the titanium nitride film so that laminations of thetitanium film, the titanium nitride film and the tungsten film fill upan entire part of the contact hole. In this case, The titanium film notonly extends on the vertical inner wall of the contact hole but alsofills up the one end of the contact hole.

It is available that the reservoir portion has a horizontal section areawhich is nearly equal to a vertical section area of the interconnectionlayer.

It is available that the reservoir portion has a vertical length whichis substantially equal to or larger than a thickness of theinterconnection layer.

It is available to further provide an additional interconnection layerextending within the insulation layer, wherein the additionalinterconnection layer has an intermediate portion which is in contactwith another end, which is opposite to the one end, of the contact layerand being made of the second conductive material. In this case, it isoptionally available that the additional interconnection layer has anadditional reservoir portion which is made of the same material as theadditional interconnection layer, wherein the additional reservoirportion extends within the insulation layer and further extends from theintermediate portion of the additional interconnection layer in thefirst vertical direction. In this case, it is also optionally availablethat the additional interconnection layer has substantially the samestructure and the same section size as the interconnection layer. Inthis case, it is also optionally available that the additional reservoirportion has substantially the same size as the reservoir portion.

The present invention also provides still another interconnectionstructure which comprises an insulation layer having a contact holewhich extends in a first vertical direction, a contact layer residingwithin the contact hole, the contact layer being made of a conductivematerial, and an interconnection layer being made of the same conductivematerial as the contact layer. The interconnection layer extends withinthe insulation layer in a horizontal direction. The interconnectionlayer has one end portion which is in contact with one end of thecontact layer so that an electron current flows on both the contactlayer and the interconnection layer. The electron current has a passagewhich is turned at an almost right angle at a boundary between thecontact layer and the interconnection layer. The electron current has ahigher current density at the boundary than other portions of both theinterconnection layer and the contact layer. The interconnection layerhas a reservoir portion which is made of the same material as theinterconnection layer. The reservoir portion extends within theinsulation layer and extends from the end portion of the interconnectionlayer in a second vertical direction which is opposite to the firstvertical direction.

If the first vertical direction is upward, then the second verticaldirection is downward. If the first vertical direction is downward, thenthe second vertical direction is upward.

It is available that the conductive material is a non-refractory metalwhich is not classified into refractory metals. In this case, thenon-refractory metal may, for example, be either Al, Cu or AlSiCu. Inthis case, it is available to further provide a titanium nitride filmwhich coats an entire surface of the interconnection layer except forthe reservoir portion, provided that the insulation layer is made ofsilicon oxide, in order to physically isolate the non-refractory metalfrom the insulation layer made of silicon oxide. It is available tofurther provide a titanium film which is interposed between the titaniumnitride film and the insulation layer made of silicon oxide.

It is available that the contact layer comprises a titanium thin filmextending at least on a vertical inner wall of the contact hole, atitanium nitride thin film extending on the titanium film, and anon-refractory metal thick film being made of the same material as theinterconnection layer. The non-refractory metal thick film resides onthe titanium nitride film so that laminations of the titanium film, thetitanium nitride film and the non-refractory metal thick film fill up anentire part of the contact hole. In this case it is available that thetitanium film not only extends on the vertical inner wall of the contacthole but also fills up the one end of the contact hole.

It is available that the contact layer comprises a refractory metal thinfilm being made of a refractory metal and extending at least on avertical inner wall of the contact hole, and a non-refractory metalthick film being made of the same material as the interconnection layerand residing on the refractory metal thin film so that laminations ofthe refractory metal thin film and the non--refractory metal thick filmfill up an entire part of the contact hole. In this case, the refractorymetal may, for example, be either tungsten or titanium.

It is available that the contact layer comprises a refractory silicidethin film being made of a refractory silicide and extending at least ona vertical inner wall of the contact hole, and a non-refractory metalthick film being made of the same material as the interconnection layerand residing on the refractory thin film, so that laminations of therefractory silicide thin film and the non-refractory metal thick filmfill up an entire part of the contact hole. In this case, the refractorysilicide may, for example, be tungsten silicide or molybdenum silicide.

It is available that the contact hole has a section area which issufficiently smaller than an section area of the interconnection layerfor further raising the current density at the boundary between thecontact layer and the interconnection layer.

It is available that the reservoir portion has a horizontal section areawhich is nearly equal to a vertical section area of the interconnectionlayer.

It is available that the reservoir portion has a vertical length whichis substantially equal to or larger than a thickness of theinterconnection layer.

It is available to further provide an additional interconnection layerextending within the insulation layer, wherein the additionalinterconnection layer has one end portion which is in contact withanother end, which is opposite to the one end, of the contact layer, andthe additional interconnection layer is made of the conductive material.In this case, it is optionally available that the additionalinterconnection layer has an additional reservoir portion which is madeof the same material as the additional interconnection layer, and alsothat the additional reservoir portion extends within the insulationlayer and further extends from the one end portion of the additionalinterconnection layer in the first vertical direction. In this case, itis also optionally available that the additional interconnection layerhas substantially the same structure and the same section size as theinterconnection layer. In this case, it is moreover available that theadditional reservoir portion has substantially the same size as thereservoir portion.

The present invention provides a further interconnection structure whichcomprises an insulation layer having a contact hole which extends in afirst vertical direction, a contact layer residing within the contacthole and being made of a conductive material, and an interconnectionlayer being made of the same conductive material as the contact layer.The interconnection layer extends within the insulation layer in ahorizontal direction. The interconnection layer has an intermediateportion which is in contact with one end of the contact layer so that anelectron current flows on both the contact layer and the interconnectionlayer. The electron current on the interconnection layer comprises twocurrents flowing in the opposite directions. The electron current has apassage which is turned at an almost right angle at a boundary betweenthe contact layer and the interconnection layer. The electron currentalso has a higher current density at the boundary than other portions ofboth the interconnection layer and the contact layer. Theinterconnection layer has a reservoir portion which is made of the samematerial as the interconnection layer. The reservoir portion extendswithin the insulation layer and extends from the intermediate portion ina second vertical direction which is opposite to the first verticaldirection.

If the first vertical direction is upward, then the second verticaldirection is downward. If the first vertical direction is downward, thenthe second vertical direction is upward.

It is available that the conductive material is a non-refractory metalwhich is not classified into refractory metals. In this case, thenon-refractory metal may, for example, be either Al, Cu and AlSiCu. Inthis case, it is available to further provide a titanium nitride filmwhich coats an entire surface of the interconnection layer except forthe reservoir portion, provided that the insulation layer is made ofsilicon oxide, in order to physically isolate the non-refractory metalfrom the insulation layer made of silicon oxide. In this case, it isavailable further provide a titanium film which is interposed betweenthe titanium nitride film and the insulation layer made of siliconoxide.

It is available that the contact layer comprises a titanium thin filmextending at least on a vertical inner wall of the contact hole, atitanium nitride thin film extending on the titanium film, and anon-refractory metal thick film being made of the same material as theinterconnection layer and residing on the titanium nitride film, so thatlaminations of the titanium film, the titanium nitride film and thenon-refractory metal thick film fill up an entire part of the contacthole. In this case, it is also available that the titanium film not onlyextends on the vertical inner wall of the contact hole but also fills upthe one end of the contact hole.

It is available that the contact layer comprises a refractory metal thinfilm being made of a refractory metal and extending at least on avertical inner wall of the contact hole, and a non-refractory metalthick film being made of the same material as the interconnection layerand residing on the refractory metal thin film, so that laminations ofthe refractory metal thin film and the non-refractory metal thick filmfill up an entire part of the contact hole. In this case, the refractorymetal may, for example, be either tungsten or titanium.

It is available that the contact layer comprises a refractory silicidethin film being made of a refractory silicide and extending at least ona vertical inner wall of the contact hole, and a non-refractory metalthick film being made of the same material as the interconnection layerand residing on the refractory thin film, so that laminations of therefractory silicide thin film and the non-refractory metal thick filmfill up an entire part of the contact hole. In this case, the refractorysilicide may, for example, be either tungsten silicide and molybdenumsilicide.

It is available that the contact hole has a section area which issufficiently smaller than an section area of the interconnection layerfor further raising the current density at the boundary between thecontact layer and the interconnection layer.

It is available that the reservoir portion has a horizontal section areawhich is nearly equal to a vertical section area of the interconnectionlayer.

It is available that the reservoir portion has a vertical length whichis substantially equal to or larger than a thickness of theinterconnection layer.

It is available to further provide an additional interconnection layerextending within the insulation layer and having an intermediate portionwhich is in contact with another end, which is opposite to the one end,of the contact layer, wherein the additional interconnection layer ismade of tile conductive material. In this case, it is optionallyavailable that the additional interconnection layer has an additionalreservoir portion which is made of the same material as the additionalinterconnection layer, and also that the additional reservoir portionextends within the insulation layer and further extends from theintermediate portion of the additional interconnection layer in thefirst vertical direction. In this case, it is available that theadditional interconnection layer has substantially the same structureand the same section size as the interconnection layer. In this case, itis available that the additional reservoir portion has substantially thesame size as the reservoir portion.

The present invention provides a still further interconnection structurewhich comprises an insulation layer having a contact hole which extendsin a first vertical direction, a contact layer being provided within thecontact hole to fill up the contact hole, and an interconnection layer.The contact layer further comprises first, second and third contactfilms. The first contact film both extends on a vertical inner wall ofthe contact hole and resides to fill up one end of the contact hole. Thefirst contact film is made of a first conductive material having a firstelectromigration resistance. The second contact film extends on thefirst contact film and is made of a second conductive material having asecond electromigration resistance which is higher than the firstelectromigration resistance. The third contact film extends on thesecond contact film so that laminations of the first, second and thirdcontact films fill up an entire part of the contact hole The thirdcontact film is made of a third conductive material having a thirdelectromigration resistance which is substantially equal to or smallerthan the second electromigration resistance. The interconnection layerextends within the insulation layer and has one end portion which isconnected with the contact layer so that the interconnection layer is incontact with the first contact film. The interconnection layer is madeof the first conductive material.

If the first vertical direction is upward, then the second verticaldirection is downward. If the first vertical direction is downward, thenthe second vertical direction is upward.

It is available that the first conductive material is a non-refractorymetal which is not classified into refractory metals. In this case, thenon-refractory metal may, for example, be Al, Cu and AlSiCu.

It is available that the second conductive material is a refractorymetal.

It is available that the second conductive material is titanium nitride.

It is available that the second conductive film comprises laminations ofa titanium film and a titanium nitride film.

It is available that the second conductive material is a refractorysilicide.

It is available that the third conductive material is a refractorymetal.

It is available that the third conductive material is the same as thefirst conductive material.

It is available that the interconnection layer has a reservoir portionwhich is made of the same material as the interconnection layer, andthat the reservoir portion extends within the insulation layer andextends from the one end portion of the interconnection layer in asecond vertical direction which is opposite to the first verticaldirection. In this case, it is optionally available that the reservoirportion has a horizontal section area which is nearly equal to avertical section area of the interconnection layer. In this case, it isalso available that the reservoir portion has a vertical length which issubstantially equal to or larger than a thickness of the interconnectionlayer.

It is also available to further provide a titanium nitride film whichcoats an entire surface of the interconnection layer provided that theinsulation layer is made of silicon oxide, in order to physicallyisolate the non-refractory metal from the insulation layer made ofsilicon oxide. In this case, it is available further provide a titaniumfilm which is interposed between the titanium nitride film and theinsulation layer made of silicon oxide.

It is available to further provide an additional interconnection layerextending within the insulation layer, wherein the additionalinterconnection layer has one end portion which is in contact withanother end, which is opposite to the one end, of the contact layer, andwherein the additional interconnection layer is made of the firstconductive material. In this case, it is optionally available that theadditional interconnection layer has all additional reservoir portionwhich is made of the same material as the additional interconnectionlayer, and also that the additional reservoir portion extends within theinsulation layer and further extends from the one end portion of theadditional interconnection layer in the first vertical direction. Inthis case, it is available that the additional interconnection layer hassubstantially the same structure and the same section size as theinterconnection layer. In this case, it is further available that theadditional reservoir portion has substantially the same size as thereservoir portion.

The present invention provides yet a further interconnection structurewhich comprises an insulation layer having a contact hole which extendsin a first vertical direction, a contact layer being provided within thecontact hole to fill up the contact hole, and an interconnection layer.The contact layer further comprises first, second and third contactfilms The first contact film both extends on a vertical inner wall ofthe contact hole and fills up one end of the contact hole. The firstcontact film is made of a first conductive material leaving a firstelectromigration resistance. The second contact film extends on thefirst contact film. The second contact film is made of a secondconductive material having a second electromigration resistance which ishigher than the first electromigration resistance. The third contactfilm extends on the second contact film so that laminations of thefirst, second and third contact films fill up an entire part of thecontact hole. The third contact film is made of a third conductivematerial having a third electromigration resistance which issubstantially equal to or smaller than the second electromigrationresistance. The interconnection layer extends within the insulationlayer. The interconnection layer has an intermediate portion which isconnected with the contact layer. The interconnection layer is incontact with the first contact film so that an electron current isdivided at the intermediate portion into two currents flowing on theinterconnection layer in the opposite directions. The interconnectionlayer is made of the first conductive material.

If the first vertical direction is upward, then the second verticaldirection is downward. If the first vertical direction is downward, thenthe second vertical direction is upward. The first conductive materialis a non-refractory metal which is not classified into refractorymetals. In this case, the non-refractory metal may, for example, beeither Al, Cu and AlSiCu.

It is available that the second conductive material is a refractorymetal.

It is available that the second conductive material is titanium nitride.

It is also available that the second conductive film compriseslaminations of a titanium film and a titanium nitride film.

It is further available that the second conductive material is arefractory silicide.

It is moreover available that the third conductive material is arefractory metal.

It is still further available that the third conductive material is thesame as the first conductive material.

It is yet further available that the interconnection layer has areservoir portion which is made of the same material as theinterconnection layer, and also that the reservoir portion extendswithin the insulation layer and extends from the one end portion of theinterconnection layer in a second vertical direction which is oppositeto the first vertical direction. In this case, it is available that thereservoir portion has a horizontal section area which is nearly equal toa vertical section area of the interconnection layer. In this case, itis available that the reservoir portion has a vertical length which issubstantially equal to or larger than a thickness of the interconnectionlayer.

It is available to further provide a titanium nitride film which coatsan entire surface of the interconnection layer, provided that theinsulation layer is made of silicon oxide, in order to physicallyisolate the non-refractory metal from the insulation layer made ofsilicon oxide. In this case, it is available to further provide atitanium film which is interposed between the titanium nitride film andthe insulation layer made of silicon oxide.

It is further available to further provide an additional interconnectionlayer extending within the insulation layer, wherein the additionalinterconnection layer has one end portion which is in contact withanother end, which is opposite to the one end, of the contact layer, andwherein the additional interconnection layer is made of the firstconductive material. In this case, it is optionally available that theadditional interconnection layer has an additional reservoir portionwhich is made of the same material as the additional interconnectionlayer, and also that the additional reservoir portion extends within theinsulation layer and further extends from the one end portion of theadditional interconnection layer in the first vertical direction. Inthis case, it is also optionally available that the additionalinterconnection layer has substantially the same structure and the samesection size as the interconnection layer. In this case, it is furtheroptionally available that the additional reservoir portion hassubstantially the same size as the reservoir portion.

According to the present inventions the reservoir portion and thecontact hole extend from the end portion of the interconnection layer inthe upward and downward directions, namely the opposite directions. Thereservoir portion has the same plane size as the interconnection layer.In the plane view, the reservoir portion is included in theinterconnection layer without extending outside the interconnection.This means that providing the reservoir results in no increase in thenecessary area thereby allowing a high density integration. Further, thesecondary reservoir, the aluminum film is provided within the contacthole. This means that providing the secondary reservoir results in noincrease in the necessary area thereby allowing a high densityintegration.

Both the reservoir and secondary reservoir supply aluminum atoms to theend portion of the aluminum film of the interconnection layer. Whenelectron currents flow from the contact layer to the aluminum film ofthe interconnection layer, then any void is likely to be formed due toelectromigration in the aluminum film near a boundary between thealuminum film and the tungsten plug or the titanium nitride film sincealuminum has a smaller electromigration resistance than that of tungstenor titanium nitride. If, however, any void is about to be formed due toelectromigration, then immediately aluminum atoms in the reservoirportion move or migrate toward the position at which a void is about tobe formed. Whilst aluminum atoms migrate from the boundary region alongthe electron current, a sufficient amount of fresh aluminum atoms aresupplied from the reservoir portion to the boundary portion, to thetungsten film, of the aluminum film. For this reason, almost no void isformed due to electromigration. Accordingly, providing the reservoirportion near the boundary between the aluminum film and the tungstenplug or titanium nitride can prevent any formation of void due toelectromigration for the above reason. Further, the reservoir portion isprovided so that no part of the reservoir portion extends outwardly fromthe interconnection layers in horizontal directions. Needless to say,this structural condition is very important for realizing a possiblehigh density integration in the two dimensional direction of thesemiconductor device including multilevel interconnections. Therefore,the reservoir portion with the secondary reservoir portion of thepresent invention provides two very important effects, or not onlyprevents any formation of void due to electromigration, but also allowsa possible high density integration in the two dimensional direction.

EMBODIMENTS

A first embodiment according to the present invention will be describedwith reference to FIGS. 4A through 4E, wherein a novel structure ofmultilevel interconnection layers extending within inter-layerinsulators and being connected to each other through a contact layer.The novel multilevel interconnection layers are structurally andphysically improved not only to allow a high density integration of theinterconnection layers but also to prevent any void formation due toelectromigration of aluminum atoms in the interconnection layers.

The structure of the novel multilevel interconnection layers will bedescribed with reference to FIG. 4E. Field oxide films 2 are selectivelyformed on a top surface of a silicon substrate 1 so that a passiveregion is defined as a region on which the field oxide films are formedand an active region is defined as a region on which no field oxide filmis formed. A first inter-layer insulator 3 extends both on the fieldoxide film 2 and the active region of the silicon substrate 1. A firstcontact hole is provided which vertically extends from the active regionof the silicon substrate 1 to the top surface of the first inter-layerinsulator 3. The first contact hole has the bottom portion and a sidewall, both of which are covered by a titanium film. A titanium nitridefilm is provided which extends on the titanium film. A tungsten plug isprovided on the titanium nitride film so that the first contact hole isfilled up both with the laminations of the titanium film and thetitanium nitride film and with the tungsten plug.

A silicon oxide film 12 is provided on the first inter-layer insulator3. A silicon oxide film 14 is provided on the silicon oxide film 12 sothat the silicon oxide films 12 and 14 constitute a second inter-layerinsulator. A first interconnection layer almost horizontally extends onthe first inter-layer insulator and within the silicon oxide film 12.The fist interconnection layer comprises an aluminum film 9 coated by atitanium nitride film and by the laminations of the titanium film andthe titanium nitride film. The first interconnection layer has a firstend portion which is in contact with the top portion of the firstcontact layer within the first contact hole. The first contact layerextends downward from the first end portion of the first interconnectionlayer. The first end portion of the first interconnection layer also hasa first reservoir portion which extends therefrom upwardly. The firstreservoir portion is made of aluminum and is which contact directly withthe aluminum film of the first interconnection layer. The firstreservoir portion has the top which reaches an interface between thesilicon oxide film 12 and a silicon oxide film 14 extending on thesilicon oxide film 12. The first reservoir portion and the first contacthole extend from the first end portion of the first interconnectionlayer in the upward and downward directions, namely the oppositedirections. The first reservoir portion has the same plane size as thefirst interconnection layer. In the plan view, the first reservoirportion is included in the first interconnection layer without extendingoutside the first interconnection. This means that providing thereservoir results in no increase in the necessary area thereby allowinga high density integration. The first reservoir is to supply aluminumatoms to the first end portion of the aluminum film 9 of the firstinterconnection layer. When electron currents flow from the firstcontact layer to the aluminum film of the first interconnection layer,then any void is likely to be formed due to electromigration in thealuminum film near a boundary between the aluminum film and the tungstenplug since aluminum has a smaller electromigration resistance than thatof tungsten. If, however, any void is about to be formed due toelectromigration, then immediately aluminum atoms in the reservoirportion move toward the position at which a void is about to be formed.Whilst aluminum atoms migrate from the boundary region along theelectron current, a sufficient amount of fresh aluminum atoms aresupplied from the reservoir portion to the boundary portion, to thetungsten film, of the aluminum film. For this reason, almost no void isformed due to electromigration. Accordingly, providing the reservoirportion near the boundary between the aluminum film and the tungstenplug can prevent any formation of void due to electromigration for theabove reason.

The first interconnection layer has a second end portion which is incontact with a second contact layer provided within a second contacthole. The second contact hole extends upward from the second end portionof the first interconnection layer. The second end portion of the firstinterconnection layer also has a second reservoir portion which extendstherefrom downward. The second reservoir portion is made of aluminum andis which contact directly with the aluminum film of the firstinterconnection layer. The second reservoir portion and the secondcontact hole extend from the second end portion of the firstinterconnection layer in the downward and upward directions, namely theopposite directions. The second reservoir portion has the same plan sizeas the first interconnection layer. In the plan view, the secondreservoir portion is included in the first interconnection layer withoutextending outside the first interconnection. This means that providingthe reservoir results in no increase in the necessary area therebyallowing a high density integration. The second reservoir is to supplyaluminum atoms to the second end portion of the aluminum film 9 of thefirst interconnection layer. When electron currents flow from the secondcontact layer to the aluminum film of the first interconnection layer,then any void is likely to be formed due to electromigration in thealuminum film near a boundary between the aluminum fill and the tungstenplug since aluminum has a smaller electromigration resistance than thatof titanium nitride film. If, however, any void is about to be formeddue to electromigration, then immediately aluminum atoms in thereservoir portion move toward the position at which a void is about tobe formed. Whilst aluminum atoms migrate from the boundary region alongthe electron current, a sufficient amount of fresh aluminum atoms aresupplied from the reservoir portion to the boundary portion, to thetitanium nitride film, of the aluminum film. For this reason, almost novoid is formed due to electromigration. Accordingly, providing thereservoir portion near the boundary between the aluminum film and thetitanium nitrides can prevent any formation of void due toelectromigration for the above reason. A second interconnection layerextends on the silicon oxide film 14. The second interconnection layerhas the same structure as the first interconnection layer. The first andsecond interconnection layers are connected to each other through thesecond contact layer. The second interconnection layer has a first endportion which is in contact with the top of the second contact layer.The first end portion of the second interconnection layer has a thirdreservoir portion 22 which is made of aluminum. The third reservoirportion 22 extends upward from the first end portion of the secondinterconnection layer 20. The third reservoir portion 22 and the secondcontact hole extend upward and downward from the first end portion ofthe second interconnection layer 20. The third reservoir portion has thesane role as the first reservoir, for which reason the descriptionsthereof will be omitted. The second interconnection layer 20 has thesame structure and the first interconnection layer. For example, thesecond interconnection layer 20 comprises an aluminum film 18 coatedboth by a titanium nitride film 19 and by laminations of a titanium film15 and a titanium nitride film 16. The second interconnection layer 20extends within a silicon oxide film 21. A silicon oxide film 23 extendsto cover the silicon oxide film 21 and the third reservoir.

As described above, the reservoir portion and the contact hole extendfrom the end portion of the interconnection layer in the upward anddownward directions, namely the opposite directions. The reservoirportion has the same plane size as the interconnection layer. In theplane view, the reservoir portion is included in the interconnectionlayer without extending outside the interconnection. This means thatproviding the reservoir results in no increase in the necessary areathereby allowing a high density integration.

The reservoir supplies aluminum atoms to the end portion of the aluminumfilm of the interconnection layer. When electron currents flow from thecontact layer to the aluminum film of the interconnection layer, thenany void is likely to be formed due to electromigration in the aluminumfilm near a boundary between the aluminum film and the tungsten plug orthe titanium nitride film since aluminum has a smaller electromigrationresistance than that of tungsten or titanium nitride. If, however, anyvoid is about to be formed due to electromigration, then immediatelyaluminum atoms in the reservoir portion move or migrate toward theposition at which a void is about to be formed. Whilst aluminum atomsmigrate from the boundary region along the electron current, asufficient amount of fresh aluminum atoms are supplied from thereservoir portion to the boundary portion, to the tungsten film, of thealuminum film. For this reason, almost no void is formed due toelectromigration. Accordingly, providing the reservoir portion near theboundary between the aluminum film and the tungsten plug or titaniumnitride can prevent any formation of void due to electromigration forthe above reason. Further, the reservoir portion is provided so that nopart of the reservoir portion extends outwardly from the interconnectionlayers in horizontal directions. Needless to say, this structuralcondition is very important for realizing a possible high densityintegration in the two dimensional direction of the semiconductor deviceincluding multilevel interconnections. Therefore, the reservoir portionof the present invention provides two very important effects, or notonly prevents any formation of void due to electromigration, but alsoallows a possible high density integration in the two dimensionaldirection.

The above novel multilevel interconnection layers may be fabricated asfollows. As illustrated in FIG. 4A, a silicon substrate 1 is preparedand then subjected to a local oxidation of silicon to selectively form afield oxide film 2 on a top surface of the silicon substrate 1. Thefield oxide film 2 is formed on a passive region and an active region isnot covered by the field oxide film 2. The selective formation of thefield oxide film 2 defines the active legion. A silicon oxide filmhaving a thickness of 150 nanometers is formed on an entire surface ofthe substrate to cover both the field oxide film 2 and the active regionof the silicon substrate 1. Further, a boron phosphate silicate glassfilm (BPSG film) having a thickness of 650 nanometers is deposited on anentire surface of the silicon oxide film so as to form a firstinter-layer insulator 3. The first inter-layer insulator 3 isselectively etched to form a first contact hole 4 over the active regionof the silicon substrate 1. As a result, a part of the active region,not covered by the field oxide film 2, of the silicon substrate 1 isexposed through the first contact hole 4.

As illustrated in FIG. 4B, a titanium film 5 having a thickness of 60nanometers is deposited by sputtering on an entire surface of thesubstrate so that the titanium film 5 extends on the top surface of thefirst inter-layer insulator 3 and further extends both on a verticalside wall of the first contact hole 4 and on the bottom of the firstcontact hole 4 so that the titanium film 5 at the bottom of the firstcontact hole 4 is in contact with a part of the top surface on theactive region of the silicon substrate 1. A titanium nitride film 6having a thickness of 100 nanometers is deposited by sputtering on anentire surface of the titanium film 5. As a result, the titanium nitridefilm 6 extends in an almost horizontal direction over the firstinter-layer insulator and further resides within the first contact hole4. Laminations of the titanium film 5 and the titanium nitride film 6serve as a barrier layer. A tungsten film is deposited by a chemicalvapor deposition method on an entire surface of the titanium nitridefilm 6 so that the tungsten film not only extends over the firstinter-layer insulator 3 but also reside within the first contact hole 4to fill up the contact hole 4 with the tungsten film, the titaniumnitride film 6 and the titanium film 5. The tungsten film deposited isthen subjected to en etch back in order to leave the tungsten film onlywithin the first contact hole 4. The remaining part of the tungsten film7 serves as a tungsten plug 7. The laminations of the titanium nitridefilm 6 and the titanium film 5 are selectively removed by a reactiveion-etching which uses a mixture gas of CHF₃ and O₂. Subsequently, thefirst inter-layer insulator 3 is also selectively removed by a reactiveion-etching which uses a mixture gas of CHF₃ and O₂ so as to form afirst aperture 8 over the field oxide film 2. The first aperture 8extends vertically from the titanium nitride film 6 through the titaniumfilm 5 into the first inter-layer insulator 3, provided the bottom ofthe first aperture 8 does not reach an interface between the firstinter-layer insulator 3 and the field oxide film 2. The bottom of thefirst aperture 8 is separated by the first inter-layer insulator 3 fromthe top of the field oxide film 2.

As illustrated in FIG. 4C, an aluminum film 9 having a thickness 450nanometers is entirely deposited by sputtering not only on the titaniumnitride film 6 but also within the first aperture 8. Subsequently, thedeposited aluminum film 9 is subjected to a heat treatment at atemperature of 450° C. so that the deposited aluminum 9 shows a reflowand thus the first aperture 8 is filled up with the aluminum firm 9. Atitanium film 10 having a thickness of 50 nanometers is deposited bysputtering on an entire surface of the aluminum film 9. The titaniumnitride film 10, the aluminum film 9, the titanium nitride film 6 andthe titanium film 5 are sequentially and selectively etched and thuspatterned to thereby form a first interconnection layer 11. The firstinterconnection layer is connected to the active region of the siliconsubstrate 1 via the first contact hole 4.

As illustrated in FIG. 4D, a silicon oxide film 12 having a thickness ofapproximately 1.2 micrometers is deposited by a plasma chemical vapordeposition on an entire surface of the substrate so that the siliconoxide film 12 covers the first interconnection layer 11 and the topsurface of the first inter-layer insulator 12. Subsequently, thedeposited silicon oxide film 12 is planarized by chemical or mechanicalpolishing so that the silicon oxide film 12 over the firstinterconnection layer has a thickness of 400 nanometers. The siliconoxide film 12 and the titanium nitride film 10 arc selectively etched toform a second aperture over the first contact hole 4 so that thealuminum film 9 is exposed through the second aperture. An aluminum film13 having a thickness of 800 nanometers is entirely deposited bysputtering both on the top surface of the silicon oxide film 12 andwithin the second aperture. The deposited aluminum film 13 is subjectedto a heat treatment at a temperature of 450° C. to cause a reflow of thealuminum film 13. As a result, the second aperture is filled up with thealuminum film 13. The aluminum film 13 is selectively removed by achemical and mechanical polishing to leave the aluminum film 13 onlywithin the second aperture. A silicon oxide film 14 having a thicknessof 400 nanometers is deposited by sputtering on the silicon oxide film12 and on the aluminum fill 13 so as to form a second inter-layerinsulator which comprises the silicon oxide film 12 and the siliconoxide film 14. The second inter-layer insulator is selectively etched bya reactive ion-etching which uses a mixture gas of CHF₃ and O₂ so as toform a second contact hole over the first aperture. As a result, a partof the titanium nitride film 10 on the aluminum layer 9 is exposedthrough the second contact hole. A titanium film 15 having a thicknessof 30 nanometers is entirely deposited by sputtering on a top surface ofthe silicon oxide film 14 and further on both a vertical wall and abottom of the second contact hole so that the titanium film 15 is incontact with the titanium nitride film 10 covering the aluminum film 9.A titanium nitride film 16 having a thickness of 100 nanometers isdeposited by sputtering on an entire surface of the titanium film 15 sothat the titanium nitride film 16 extends over the silicon oxide film 14and within the second contact hole. A tungsten film is entirelydeposited by chemical vapor deposition on the titanium nitride film 16so that the tungsten film extends over the silicon oxide film 14 andresides within the second contact hole, wherein the second contact holeis filled up with the tungsten film and the laminations of the titaniumfilm 15 and the titanium nitride film 16. The deposited tungsten film issubjected to etch back so that the tungsten film remains only within thesecond contact hole. The remaining part of the tungsten film serves as atungsten plug 17. An aluminum film 18 having a thickness of 600nanometers is entirely deposited both on the titanium nitride film 16and on the tungsten plug 17. A titanium nitride film 19 having athickness of 50 nanometers is entirely deposited by sputtering on thealuminum film 18 The titanium nitride film 19, the aluminum film 18, thetitanium nitride film 15 and the titanium film 14 are selectively etchedand thus patterned to form a second interconnection layer 20 whichcomprises the titanium film 15, the titanium nitride film 16, thealuminum film 18 and the titanium nitride film 19.

As illustrated in FIG. 4E, a silicon oxide film 21 having a thickness ofabout 2.1 micrometers is entirely deposited by a plasma chemical vapordeposition to cover the second inter-layer insulator 20 and the siliconoxide film 14. The deposited silicon oxide film 21 is then plagiarizedby a chemical and mechanical polishing so that the silicon oxide film 21over the second interconnection layer 20 has a thickness of 400nanometers. The plagiarized silicon oxide film 21 and the titaniumnitride film 19 are selectively etched by a reactive ion-etching whichuses CHF₃ and O₂ to form a third aperture over the second contact holeso that a part of the aluminum film 18 is exposed through the thirdaperture. An aluminum film 22 is deposited on the silicon oxide film 21and within the third aperture. The deposited aluminum film 22 is thensubjected to a heat treatment at a temperature of 450° C. to cause areflow of the aluminum film 22 so that the third aperture is filled upwith the aluminum film 22. The aluminum film 22 is then selectivelyremoved by a chemical and mechanical polishing so as to leave thealuminum film 22 only within the third aperture. A silicon oxide film 23having a thickness of 500 nanometers is entirely deposited by a plasmachemical vapor deposition on the silicon oxide film 23 and the aluminumfilm 22. The deposited silicon oxide film 23 serves as a protectionfilm.

A second embodiment according to the present invention will be describedwith reference to FIGS. 5A through SE, wherein a novel structure ofmultilevel interconnection layers extending within inter-layerinsulators and being connected to each other through a contact layer.The novel multilevel interconnection layers are structurally andphysically improved not only to allow a high density integration of theinterconnection layers but also to prevent any void formation due toelectromigration of aluminum atoms in the interconnection layers.

The structure of the novel multilevel interconnection layers will bedescribed with reference to FIG. 5E. Field oxide films 2 are selectivelyformed on a top surface of a silicon substrate 1 so that a passiveregion is defined as a region on which the field oxide films are formedand an active region is defined as a region on which no field oxide filmis formed. A first inter-layer insulator 3 extends both on the fieldoxide film 2 and the active region of the silicon substrate 1. A firstcontact hole is provided which vertically extends from the active regionof the silicon substrate 1 to the top surface of the first inter-layerinsulator 3. The first contact hole has the bottom portion and a sidewall, both of which are covered by a titanium film. A titanium nitridefilm is provided which extends on the titanium film. A tungsten plug isprovided on the titanium nitride film so that the first contact hole isfilled up both with the laminations of the titanium film and thetitanium nitride film and with the tungsten plug.

A silicon oxide film 12 is provided on the first inter-layer insulator3. A silicon oxide film 14 is provided on the silicon oxide film 12 sothat the silicon oxide films 12 and 14 constitute a second inter-layerinsulator. A first interconnection layer almost horizontally extends onthe first inter-layer insulator and within the silicon oxide film 12.The first interconnection layer comprises an aluminum film 9 coated by atitanium nitride film and by the laminations of the titanium film andthe titanium nitride film. The first interconnection layer has a firstend portion which is in contact with the top, portion of the firstcontact layer within the first contact hole. Tie first contact layerextends downward from the first end portion of the first interconnectionlayer. The first end portion of the first interconnection layer also hasa first reservoir portion which extends therefrom upwardly. The firstreservoir portion is made of aluminum and which is in contact directlywith the aluminum film of the first interconnection layer. The firstreservoir portion has the top which reaches an interface between thesilicon oxide film 12 and a silicon oxide film 14 extending on thesilicon oxide film 12. The first reservoir portion and the first contacthole extend from the first end portion of the first interconnectionlayer in tile upward and downward directions, namely the oppositedirections. The first reservoir portion has the same plane size as thefirst interconnection layer. In the plane view, the first reservoirportion is included in the first interconnection layer without extendingoutside the first interconnection. This means that providing thereservoir results in no increase in the necessary area thereby allowinga high density integration. The first reservoir is to supply aluminumatoms to the first end portion of the aluminum film 9 of the firstinterconnection layer. When electron currents flow from the firstcontact layer to the aluminum film of the first interconnection layer,then any void is likely to be formed due to electromigration in thealuminum film near a boundary between the aluminum film and the tungstenplug since aluminum has a smaller electromigration resistance than thatof tungsten. If, however, any void is about to be formed due toelectromigration, then immediately aluminum atoms in the reservoirportion move toward the position at which a void is about to be formed.Whilst aluminum atoms migrate from the boundary region along theelectron current, a sufficient amount of fresh aluminum atoms aresupplied from the reservoir portion to the boundary portions to thetungsten film, of the aluminum film. For this reason, almost no void isformed due to electromigration. Accordingly, providing the reservoirportion near the boundary between the aluminum film and the tungstenplug can prevent any formation of void due to electromigration for theabove reason.

The first interconnection layer has a second end portion which is incontact with a second contact layer provided within a second contacthole. The second contact layer includes a secondary reservoir made ofaluminum separately from a second reservoir portion which extendsdownward from the second end of the first interconnection layer. Thesecond contact hole extends upward from the second end portion of thefirst interconnection layer. The second contact layer structurallydiffers from the first contact layer. The second contact layer comprisesan aluminum film which extends on a vertical side wall of the secondcontact hole and residing at a bottom of the second contact hole. Atitanium film 25 extends on the aluminum film. A titanium nitride film26 extends on the titanium film 25. A tungsten plug is provided withinthe second contact hole so that the second contact hole is filled upwith the aluminum film 24, the titanium film 25, the titanium nitridefilm 26 and the tungsten plug 27. If the electron current flows from thesecond contact film to the first interconnection layer, a part of theelectron current flows across the titanium film 25 and the titaniumnitride film 26. This electron current may cause a formation of a voidin the aluminum film 24 at the bottom of the second contact hole. Ifsuch void is about to be formed due to electromigration in the aluminumfilm at the bottom of the second contact hole, then aluminum atoms aresupplied from not only the second reservoir but also the aluminum film24. Aluminum atoms in the aluminum film 24 migrate from the verticalportion of the aluminum film to the bottom part thereof. This ensuresprevention of any formation of the void due to electromigration. Asilicon oxide film 30 extends on the second interconnection layer and onthe silicon oxide film 24. A silicon oxide nitride film 31 is providedto cover the silicon oxide film 31.

As described above, the reservoir portion and the contact hole extendfrom the end portion of the interconnection layer in the upward anddownward directions, namely the opposite directions. The reservoirportion has the same plane size as the interconnection layer. In theplane view, the reservoir portion is included in the interconnectionlayer without extending outside the interconnection. This means thatproviding the reservoir results in no increase in the necessary areathereby allowing a high density integration. Further, the secondaryreservoir, the aluminum film 24 is provided within the contact hole.This means that providing the secondary reservoir results in no increasein the necessary area thereby allowing a high density integration.

Both the reservoir and secondary reservoir supply aluminum atoms to theend portion of the aluminum film of the interconnection layer. Whenelectron currents flow from the contact layer to the aluminum film ofthe interconnection layer, then any void is likely to be formed due toelectromigration in the aluminum film near a boundary between thealuminum film and the tungsten plug or the titanium nitride film sincealuminum has a smaller electromigration resistance than that of tungstenor titanium nitride. If, however, any void is about to be formed due toelectromigration, then immediately aluminum atoms in the reservoirportion move or migrate toward the position at which a void is about tobe formed. Whilst aluminum atoms migrate from the boundary region alongthe electron current, a sufficient amount of fresh aluminum atoms aresupplied from the reservoir portion to the boundary portion, to thetungsten film, of the aluminum film. For this reason, almost no void isformed due to electromigration. Accordingly, providing the reservoirportion near the boundary between the aluminum film and the tungstenplug or titanium nitride can prevent any formation of void due toelectromigration for the above reason. Further, the reservoir portion isprovided so that no part of the reservoir portion extends outwardly fromthe interconnection layers in horizontal directions. Needless to say,this structural condition is very important for realizing a possiblehigh density integration in the two dimensional direction of thesemiconductor device including multilevel interconnections. Therefore,the reservoir portion with the secondary reservoir portion of thepresent invention provides two very important effects, or not onlyprevents any formation of void due to electromigration, but also allowsa possible high density integration in the two dimensional direction.

The above novel multilevel interconnection layers may be fabricated asfollows. As illustrated in FIG. 5A, a silicon substrate 1 is preparedand then subjected to a local oxidation of silicon to selectively form afield oxide film 2 on a top surface of the silicon substrate 1. Thefield oxide film 2 is formed on a passive region and an active region isnot covered by the field oxide film 2. The selective formation of thefield oxide film 2 defines the active region. A silicon oxide filmhaving a thickness of 150 nanometers is formed on an entire surface ofthe substrate to cover both the field oxide film 2 and the active regionof the silicon substrate 1. Further, a boron phosphate silicate glassfilm (BPSG film) having a thickness of 650 nanometers is deposited on anentire surface of the silicon oxide film so as to form a firstinter-layer insulator 3. The first inter-layer insulator 3 isselectively etched to form a first contact Hole 4 over the active regionof the silicon substrate 1. As a result, a part of the active region,not covered by the field oxide film 2, of the silicon substrate 1 isexposed through the first contact hole 4.

As illustrated in FIG. 5B, a titanium film 5 having a thickness of 60nanometers is deposited by sputtering on an entire surface of thesubstrate so that the titanium film 5 extends on the top surface of thefirst inter-layer insulator 3 and further extends both on a verticalside wall of the first contact hole 4 and on the bottom of the firstcontact hole 4 so that the titanium film 5 at the bottom of the firstcontact hole 4 is in contact with a part of the top surface on theactive region of the silicon substrate 1. A titanium nitride film 6having a thickness of 100 nanometers is deposited by sputtering on anentire surface of tile titanium film 5. As a result, the titaniumnitride film 6 extends in an almost horizontal direction over the firstinter-layer insulator and further resides within the first contact hole4. Laminations of the titanium film 5 and the titanium nitride film 6serve as a barrier layer. A tungsten film is deposited by a chemicalvapor deposition method on an entire surface of the titanium nitridefilm 6 so that the tungsten film not only extends over the firstinter-layer insulator 3 but also reside within the first contact hole 4to fill up the contact hole 4 with the tungsten film, the titaniumnitride film 6 and the titanium film 5. The tungsten film deposited isthen subjected to en etch back in order to leave the tungsten film onlywithin the first contact hole 4. The remaining part of the tungsten film7 serves as a tungsten plug 7. The laminations of the titanium nitridefilm 6 and the titanium film 5 are selectively removed by a reactiveion-etching which uses a mixture gas of CHF₃ and O₂. Subsequently, thefirst inter-layer insulator 3 is also selectively removed by a reactiveion-etching which uses a mixture gas of CHF₃ and O₂ so as to form afirst aperture 8 over the field oxide film 2. The first aperture 8extends vertically from the titanium nitride film 6 through the titaniumfilm 5 into the first inter-layer insulator 3, provided the bottom ofthe first aperture 8 does not reach an interface between the firstinter-layer insulator 3 and the field oxide film 2. The bottom of thefirst aperture 8 is separated by the first inter-layer insulator 3 fromthe top of the field oxide film 2.

As illustrated in FIG. 5C, an aluminum film 9 having a thickness 450nanometers is entirely deposited by sputtering not only on the titaniumnitride film 6 but also within the first aperture 8. Subsequently, thedeposited aluminum film 9 is subjected to a heat treatment at atemperature of 450° C. so that the deposited aluminum 9 shows a reflowand thus the first aperture 8 is filled up with the aluminum film 9. Atitanium film 10 having a thickness of 50 nanometers is deposited bysputtering on an entire surface of the aluminum film 9. The titaniumnitride film 10, the aluminum film 9, the titanium nitride film 6 andthe titanium film 5 are sequentially and selectively etched and thuspatterned to thereby form a first interconnection layer 11. The firstinterconnection layer is connected to the active region of the siliconsubstrate 1 via the first contact hole 4.

As illustrated in FIG. 5D, a silicon oxide film 12 having a thickness ofapproximately 1.2 micrometers is deposited by a plasma chemical vapordeposition on all entire surface of the substrate so that the siliconoxide film 12 covers the first interconnection layer 11 and the topsurface of the first inter-layer insulator 12. Subsequently, thedeposited silicon oxide film 12 is plagiarized by chemical or mechanicalpolishing so that the silicon oxide film 12 over the firstinterconnection layer has a thickness of 400 nanometers. The siliconoxide film 12 and the titanium nitride film 10 are selectively etched toform a second aperture over the first contact hole 4 so that thealuminum film 9 is exposed through the second aperture. An aluminum film13 having a thickness of 800 nanometers is entirely deposited bysputtering both on the top surface of the silicon oxide film 12 andwithin the second aperture. The deposited aluminum film 13 is subjectedto a heat treatment at a temperature of 450° C. to cause a reflow of thealuminum film 13. As a result, the second aperture is filled up with thealuminum film 13. The aluminum film 13 is selectively removed by achemical and mechanical polishing to leave the aluminum film 13 onlywithin the second aperture. A silicon oxide film 14 having a thicknessof 400 nanometers is deposited by sputtering on the silicon oxide film12 and on the aluminum film 13 so as to form a second inter-layerinsulator which comprises the silicon oxide film 2 and the silicon oxidefilm 14. The second inter-layer insulator is selectively etched by areactive ion-etching which uses a mixture gas of CHF₃ and O₂ so as tofont a second contact hole over the first aperture. As a result, a partof the titanium nitride film 10 on the aluminum layer 9 is exposedthrough the second contact hole. An aluminum film 24 having a thicknessof 200 nanometers is entirely deposited by sputtering not only on thetop surface of the silicon oxide film 14 but also on both a verticalside wall and a bottom of the second contact hole so that the aluminumfilm 24 at the bottom of the second contact hole is in contact with thealuminum film 9. The deposited aluminum film 24 is subjected to a heattreatment at a temperature of 450° C. to cause a reflow of the aluminumfilm 24. The thickness of the aluminum film 24 at the bottom of thecontact hole is increased by the reflow. The increase in thickness ofthe aluminum film 24 at the bottom of the contact hole both prevents anydisconnection and keeps the conformable shape at the bottom of thecontact hole. A titanium film 25 having a thickness of 30 nanometers isentirely deposited by sputtering on a top surface of the aluminum film24. The above conformable shape of the aluminum film 24 at the bottom ofthe contact hole provides a good step coverage of the titanium film 25in the vicinity of the bottom of the contact hole. A titanium nitridefilm 26 having a thickness of 100 nanometers is deposited by sputteringon an entire surface of the titanium film 25. A tungsten film isentirely deposited by chemical vapor deposition on the titanium nitridefilm 26 so that the tungsten film extends over the silicon oxide film 24and resides within the second contact hole, wherein the second contacthole is filled up with the tungsten film and the laminations of thetitanium film 25 and the titanium nitride film 26. The depositedtungsten film is subjected to etch back so that the tungsten filmremains only within the second contact hole. The remaining part of thetungsten film serves as a tungsten plug 27.

As illustrated in FIG. 5E, an aluminum film 28 having a thickness of 400nanometers is entirely deposited both on the titanium nitride film 26and on the tungsten plug 27. A titanium nitride film 29 having athickness of 50 nanometers is entirely deposited by sputtering on thealuminum film 28. The titanium nitride film 29, the aluminum film 28,the titanium nitride film 26, the titanium film 25 and the aluminum film24 are selectively etched and thus patterned to form a secondinterconnection layer which comprises the aluminum film 24, the titaniumfilm 25, the titanium nitride film 26, the aluminum film 28 and thetitanium nitride film 29. A silicon oxide film 30 having a thickness of200 nanometers is entirely deposited by chemical vapor deposition tocover the second interconnection layer and the silicon oxide film 24. Asilicon oxide nitride film 31 is then entirely deposited by chemicalvapor deposition on an entire surface of the silicon oxide film 30 sothat laminations of the silicon oxide film 30 and the silicon oxidenitride film 31 serve as a protection layer.

FIG. 6 illustrates a relationship between a time until any disconnectionappears versus a voltage of aluminum within a hole. The time wasmeasured under the following conditions. The width of theinterconnection layer is 0.8 micrometers. The size of the contact holeis 0.6 micrometers×0.6 micrometers. No seat of the contact hole exist.Temperature is 250° C. The density of current is 3×105 A/cm2. There ismeasured a time until disconnection appear for a half of any samplesversus a volume of aluminum film. The time is nearly proportional to thevolume of the aluminum film.

A third embodiment according to the present invention will be describedwith reference to FIG. 7, wherein a novel structure of multilevelinterconnection layers extending within inter-layer insulators and beingconnected to each other through a contact layer. The novel multilevelinterconnection layers are structurally and physically improved not onlyto allow a high density integration of the interconnection layers butalso to prevent any void formation due to electromigration of aluminumatoms in the interconnection layers.

The structure of the novel multilevel interconnection layers isillustrated in FIG. 7 from which the interconnections structurallydiffers from that of the first embodiment in view of the second contactlayer including an aluminum film in place of tungsten plug. Any otherstructural points are the same as those of the first embodiment.

The reservoir portion and the contact hole extend from the end portionof the interconnection layer in the upward and downward directions,namely the opposite directions. The reservoir portion has the same planesize as the interconnection layer. In the plane view, the reservoirportion is included in the interconnection layer without extendingoutside the interconnection. This means that providing the reservoirresults in no increase in the necessary area thereby allowing a highdensity integration.

The reservoir supplies aluminum atoms to tie end portion of the aluminumfilm of the interconnection layer. When electron currents flow from thecontact layer to the aluminum film of the interconnection layer, thenany void is likely to be formed due to electromigration in the aluminumfilm near a boundary between the aluminum film and the tungsten plug orthe titanium nitride film since aluminum has a smaller electromigrationresistance than that of tungsten or titanium nitride. If, however, anyvoid is about to be formed due to electromigration, then immediatelyaluminum atoms in the reservoir portion move or migrate toward theposition at which a void is about to be formed. Whilst aluminum atomsmigrate from the boundary region along the electron current, asufficient amount of fresh aluminum atoms are supplied from thereservoir portion to the boundary portion, to the tungsten film, of thealuminum film. For this reason, almost no void is formed due toelectromigration. Accordingly, providing the reservoir portion near theboundary between the aluminum film and the tungsten plug or titaniumnitride can prevent any formation of a void due to electromigration forthe above reason. Further, the reservoir portion is provided so that nopart of the reservoir portion extends outwardly from the interconnectionlayers in horizontal directions. Needless to say, this structuralcondition is very important for realizing a possible high densityintegration in the two dimensional direction of the semiconductor deviceincluding multilevel interconnections. Therefore, the reservoir portionof the present invention provides two very important effects, or notonly prevents any formation of void due to electromigration, but alsoallows a possible high density integration in the two dimensionaldirection.

A fourth embodiment according to the present invention will be describedwith reference to FIG. 8, wherein, a novel structure of multilevelinterconnection layers extending within inter-layer insulators and beingconnected to each other through a contact layer. The novel multilevelinterconnection layers are structurally and physically improved not onlyto allow a high density integration of the interconnection layers butalso to prevent any void formation due to electromigration of aluminumatoms in the interconnection layers.

The structure of the novel multilevel interconnection layers isillustrated in FIG. 8 from which the interconnections structurallydiffers from that of the third embodiment in view of the first andsecond interconnection layers are connected through an aluminum filmwithout through the titanium film or the titanium nitride film. Anyother structural points are the same as those of the first embodiment.

In this case, the formation of void may be caused at a tuning point ofthe current passage where there is a current density peak.

The reservoir portion and the contact hole extend from the end portionof the interconnection layer in the upward and downward directions,namely the opposite directions. The reservoir portion has the same planesize as the interconnection layer. In the plane view, the reservoirportion is included in the interconnection layer without extendingoutside the interconnection. This means that providing the reservoirresults in no increase in the necessary area thereby allowing a highdensity integration.

The reservoir supplies aluminum atoms to the turning point of thecurrent passage of the interconnection layer. When election currentsflow from the contact layer to the aluminum film of the interconnectionlayer, then any void is likely to be formed due to electromigration inthe aluminum film near the turning point of the current passage of theinterconnection layer. If, however, any void is about to be formed dueto electromigration, then immediately aluminum atoms in the reservoirportion move or migrate toward the position at which a void is about tobe formed. Whilst aluminum atoms migrate from the timing point of thecurrent passage of the interconnection layer, a sufficient amount offresh aluminum atoms is supplied from the reservoir portion to theturning point of the current passage of the interconnection layer. Forthis reason, almost no void is formed due to electromigration.Accordingly, providing the reservoir portion near the turning point ofthe current passage of the interconnection layer can prevent anyformation of void due to electromigration for the above reason. Further,the reservoir portion is provided so that no part of the reservoirportion extends outwardly from the interconnection layers in horizontaldirections. Needless to say, this structural condition is very importantfor realizing a possible high density integration in the two dimensionaldirection of the semiconductor device including multilevelinterconnections. Therefore, the reservoir portion of the presentinvention provides two very important effects, or not only prevents anyformation of void due to electromigration, but also allows a possiblehigh density integration in the two dimensional direction.

A fifth embodiment according to the present invention will be describedwith reference to FIG. 9, wherein a novel structure of multilevelinterconnection layers extending within inter-layer insulators and beingconnected to each other through a contact layer. The novel multilevelinterconnection layers are structurally and physically improved not onlyto allow a high density integration of the interconnection layers butalso to prevent any void formation due to electromigration of aluminumatoms in the interconnection layers.

The structure of the novel multilevel interconnection layers isillustrated in FIG. 9 from which the interconnections structurallydiffers from that of the first embodiment in view of the second contactlayer including a single titanium nitride film 16. Any other structuralpoints are the same as those of the first embodiment.

The reservoir portion and the contact hole extend from the end portionof the interconnection layer in the upward and downward directions,namely the opposite directions. The reservoir portion has the same planesize as the interconnection layer. In the plane view, the reservoirportion is included in the interconnection layer without extendingoutside the interconnection. This means that providing the reservoirresults in no increase in the necessary area thereby allowing a highdensity integration.

The reservoir supplies aluminum atoms to the end portion of the aluminumfilm of the interconnection layer. When electron currents flow from thecontact layer to the aluminum film of the interconnection layer, thenany void is likely to be formed due to electromigration in the aluminumfilm near a boundary between the aluminum film and the tungsten plug orthe titanium nitride film since aluminum has a smaller electromigrationresistance than that of tungsten or titanium nitride. If, however, anyvoid is about to be formed due to electromigration, then immediatelyaluminum atoms in the reservoir portion move or migrate toward theposition at which a void is about to be formed. Whilst aluminum atomsmigrate from the boundary region along the electron current, asufficient amount of fresh aluminum atoms are supplied from thereservoir portion to the boundary portion, to the tungsten film, of thealuminum film. For this reason, almost no void is formed due toelectromigration. Accordingly, providing the reservoir portion near theboundary between the aluminum film and the tungsten plug or titaniumnitride can prevent any formation of void due to electromigration forthe above reason. Further, the reservoir portion is provided so that nopart of the reservoir portion extends outwardly from the interconnectionlayers in horizontal directions. Needless to say, this structuralcondition is very important for realizing a possible high densityintegration in the two dimensional direction of the semiconductor deviceincluding multilevel interconnections. Therefore, the reservoir portionof the present invention provides two very important effects, or notonly prevents any formation of void due to electromigration, but alsoallows a possible high density integration in the two dimensionaldirection.

A sixth embodiment according to the present invention will be describedwith reference to FIG. 10, wherein a novel structure of multilevelinterconnection layers extending within inter-layer insulators and beingconnected to each other through a contact layer. The novel multilevelinterconnection layers are structurally and physically improved not onlyto allow a high density integration of the interconnection layers butalso to prevent any void formation due to electromigration of aluminumatoms in the interconnection layers.

The structure of the novel multilevel interconnection layers isillustrated in FIG. 10 from which the interconnections structurallydiffers from that of the second embodiment in view of the second contactlayer including an aluminum film in place of tungsten plug. Any otherstructural points are the same as those of the second embodiment.

As described above, the reservoir portion and the contact hole extendfrom the end portion of the interconnection layer in the upward anddownward directions, namely the opposite directions. The reservoirportion has the same plane size as the interconnection layer. In theplane view, the reservoir portion is included in the interconnectionlayer without extending outside the interconnection. This means thatproviding the reservoir results in no increase in the necessary areathereby allowing a high density integration. Further, the secondaryreservoir, the aluminum film 24 is provided within the contact hole.This means that providing the secondary reservoir results in no increasein the necessary area thereby allowing a high density integration.

Both the reservoir and secondary reservoir supply aluminum atoms to theend portion of the aluminum film of the interconnection layer. Whenelectron currents flow from the contact layer to the aluminum film ofthe interconnection layer, then any void is likely to be formed due toelectromigration in the aluminum film near a boundary between thealuminum film and the tungsten plug or the titanium nitride film sincealuminum has a smaller electromigration resistance than that of tungstenor titanium nitride. If, however, any void is about to be formed due toelectromigration, then immediately aluminum atoms in the reservoirportion move or migrate toward the position at which a void is about tobe formed. Whilst aluminum atoms migrate from the boundary region alongthe electron current, a sufficient amount of fresh aluminum atoms aresupplied from the reservoir portion to the boundary portion, to thetungsten film, of the aluminum film. For this reason, almost no void isformed due to electromigration. Accordingly, providing the reservoirportion near the boundary between the aluminum film and the tungstenplug or titanium nitride can prevent any formation of a void due toelectromigration for the above reason. Further, the reservoir portion isprovided so that no part of the reservoir portion extends outwardly fromthe interconnection layers in horizontal directions. Needless to say,this structural condition is very important for realizing a possiblehigh density integration in the two dimensional direction of thesemiconductor device including multilevel interconnections. Therefore,the reservoir portion with the secondary reservoir portion of thepresent invention provides two very important effects, or not onlyprevents any formation of void due to electromigration, but also allowsa possible high density integration in the two dimensional direction.

A seventh embodiment according to the present invention will bedescribed with reference to FIG, 11, wherein a novel structure ofmultilevel interconnection layers extending within inter-layerinsulators and being connected to each other through a contact layer.The novel multilevel interconnection layers are structurally andphysically improved not only to allow a high density integration of theinterconnection layers but also to prevent any void formation due toelectromigration of aluminum atoms in the interconnection layers.

The structure of the novel multilevel interconnection layers isillustrated in FIG. 11 from which the interconnections structurallydiffers from that of the second embodiment in view of providing nosecond reservoir portion. Any other structural points are the same asthose of the second embodiment.

As described above, no second reservoir portion and the secondaryreservoir portion, namely the aluminum film 24 is provided within thecontact hole. This means that providing no second reservoir portionresults in reduction in the necessary area thereby improving a highdensity integration.

The secondary reservoir alone can supply aluminum atoms to the endportion of the aluminum film of the interconnection layer. When electroncurrents flow from the contact layer to the aluminum film of theinterconnection layer, then any void is likely to be formed due toelectromigration in the aluminum film near a boundary between thealuminum film and the tungsten plug or the titanium nitride film sincealuminum has a smaller electromigration resistance than that of tungstenor titanium nitride. If, however, any void is about to be formed due toelectromigration, then immediately aluminum atoms in the secondaryreservoir portion move or migrate toward the position at which a void isabout to be formed. Whilst aluminum atoms migrate from the boundaryregion along the electron current, a sufficient amount of fresh aluminumatoms are supplied from the reservoir portion to the boundary portion,to the tungsten film, of the aluminum film. For this reason, almost novoid is formed due to electromigration. Accordingly, providing thesecondary reservoir portion near the boundary between the aluminum filmand the tungsten plug or titanium nitride can prevent any formation ofvoid due to electromigration for the above reason. Further, thesecondary reservoir portion is provided so that no part of the reservoirportion extends outwardly from the interconnection layers in horizontaldirections. Needless to say, this structural condition is very importantfor realizing a possible high density integration in the two dimensionaldirection of the semiconductor device including multilevelinterconnections. Therefore, the reservoir portion with the secondaryreservoir portion of the present invention provides two very importanteffects, or not only prevents any formation of void due toelectromigration, but also allows a possible high density integration inthe two dimensional direction.

An eighth embodiment according to the present invention will bedescribed with reference to FIG. 12, wherein a novel structure ofmultilevel interconnection layers extending within inter-layerinsulators and being connected to each other through a contact layer.The novel multilevel interconnection layers are structurally andphysically improved not only to allow a high density integration of theinterconnection layers but also to prevent any void formation due toelectromigration of aluminum atoms in the interconnection layers.

The structure of the novel multilevel interconnection layers isillustrated in FIG. 12 from which the interconnections structurallydiffers from that of the second embodiment in view of providing notitanium film within the second contact hole. Any other structuralpoints are the same as those of the second embodiment.

The effect of this embodiments are substantially the same as those ofthe seventh embodiment.

A ninth embodiment according to the present invention will be describedwith reference to FIG. 13, wherein a novel structure of multilevelinterconnection layers extending within inter-layer insulators and beingconnected to each other through a contact layer. The novel multilevelinterconnection layers are structurally and physically improved not onlyto allow a high density integration of the interconnection layers butalso to prevent any void formation due to electromigration of aluminumatoms in the interconnection layers.

The structure of the novel multilevel interconnection layers isillustrated in FIG. 13 from which the interconnections structurallydiffers from that of the first embodiment in view of connecting theinterconnection layer to the contact hole at its intermediate portionexcept for the end portion. Both side portions of the interconnectionlayer serve as interconnections but not reservoir. Any other structuralpoints are the same as those of the second embodiment.

The effect of this embodiments are substantially the same as those ofthe first embodiment.

A tenth embodiment according to the present invention will be describedwith reference to FIG. 14, wherein a novel structure of multilevelinterconnection layers extending within inter-layer insulators and beingconnected to each other through a contact layer. The novel, multilevelinterconnection layers are structurally and physically improved not onlyto allow a high density integration of the interconnection layers butalso to prevent any void formation due to electromigration of aluminumatoms in the interconnection layers.

The structure of the novel multilevel interconnection layers isillustrated in FIG. 14 from which the interconnections structurallydiffers from that of the second embodiment in view of connecting theinterconnection layer to the contact hole at its intermediate portionexcept for the end portion. Both side portions of the interconnectionlayer serve as interconnections but not reservoir. Any other structuralpoints are the same as those of the second embodiment.

The effect of this embodiments are substantially the same as those ofthe second embodiment.

An eleventh embodiment according to the present invention will bedescribed with reference to FIG. 15, wherein a novel structure ofmultilevel interconnection layers extending within inter-layerinsulators and being connected to each other through a contact layer.The novel multilevel interconnection layers are structurally andphysically improved not only to allow a high density integration of theinterconnection layers but also to prevent any void formation due toelectromigration of aluminum atoms in the interconnection layers.

The structure of the novel multilevel interconnection layers isillustrated in FIG. 15 from which the interconnections structurallydiffers from that of the third embodiment in view of connecting theinterconnection layer to the contact hole at its intermediate portionexcept for the end portion. Both side portions of the interconnectionlayer serve as interconnections but not reservoir. Any other structuralpoints are the same as those of the third embodiment.

The effect of this embodiments are substantially the same as those ofthe third embodiment.

A twelfth embodiment according to the present invention will bedescribed with reference to FIG. 16, wherein a novel structure ofmultilevel interconnection layers extending within inter-layerinsulators and being connected to each other through a contact layer.The novel multilevel interconnection layers are structurally andphysically improved not only to allow a high density integration of theinterconnection layers but also to prevent any void formation due toelectromigration of aluminum atoms in the interconnection layers.

The structure of the novel multilevel interconnection layers isillustrated in FIG. 16 from which the interconnections structurallydiffers from that of the fourth embodiment in view of connecting theinterconnection layer to the contact hole at its intermediate portionexcept for the end portion. Both side portions of the interconnectionlayer serve as interconnections but not reservoir. Any other structuralpoints are the same as those of the fourth embodiment.

The effect of this embodiments are substantially the same as those ofthe fourth embodiment.

A thirteenth embodiment according to the present invention will bedescribed with reference to FIG. 17, wherein a novel structure ofmultilevel interconnection layers extending within inter-layerinsulators and being connected to each other through a contact layer.The novel multilevel interconnection layers are structurally andphysically improved not only to allow a high density integration of theinterconnection layers but also to prevent any void formation due toelectromigration of aluminum atoms in the interconnection layers.

The structure of the novel multilevel interconnection layers isillustrated in FIG. 17 from which the interconnections structurallydiffers from that of the sixth embodiment ill view of connecting theinterconnection layer to the contact hole at its intermediate portionexcept for the end portion. Both side portions of the interconnectionlayer serve as interconnections but not reservoir. Any other structuralpoints are the same as those of the sixth embodiment.

The effect of this embodiments are substantially the same as those ofthe sixth embodiment.

A fourteenth embodiment according to the present invention will bedescribed with reference to FIG. 18, wherein a novel structure ofmultilevel interconnection layers extending within inter-layerinsulators and being connected to each other through a contact layer.The novel multilevel interconnection layers are structurally andphysically improved not only to allow a high density integration of theinterconnection layers but also to prevent any void formation due toelectromigration of aluminum atoms in the interconnection layers.

The structure of the novel multilevel interconnection layers isillustrated in FIG. 18 from which the interconnections structurallydiffers from that of the seventh embodiment in view of connecting theinterconnection layer to the contact hole at its intermediate portionexcept for the end portion. Both side portions of the interconnectionlayer serve as interconnections but not reservoir. Any other structuralpoints are the same as those of the seventh embodiment.

The effect of this embodiments are substantially the same as those ofthe seventh embodiment.

Whereas modifications of the present invention will be apparent to aperson having ordinary skill in the art, to which the inventionpertains, it is to be understood that embodiments as shown and describedby way of illustrations are by no means intended to be considered in alimiting sense. Accordingly, it is to be intended to cover by claims allmodifications which fall within the spirit and scope of the invention.

What is claimed is:
 1. A method for fabricating multilevelinterconnections comprising the steps of:forming a first inter-layerinsulator on a semiconductor substrate leaving all active region and apassive region defined by a field oxide film; selectively forming afirst contact hole in said first inter-layer on said active region;forming a barrier layer on a top surface of said first inter-layerinsulator and on both a vertical side wall and a bottom of said firstcontact hole; selectively forming a refractory metal plug within saidfirst contact hole; selectively etching said barrier layer and saidfirst inter-layer insulator to form a first aperture over said fieldoxide film, said aperture extending vertically from said barrier layerto said first inter-layer insulator, said first aperture having a bottomseparated from said field oxide film; forming a first non-refractorymetal film both on said first inter-layer insulator and within saidfirst aperture to form a first interconnection layer; subjecting saidfirst non-refractory metal film to a heat treatment to cause a reflow ofsaid first non-refractory metal film so that said first aperture isfilled up with said first non-refractory metal film; patterning saidfirst non-refractory metal film and said barrier layer; forming a secondinter-layer insulator both on said first interconnection layer and saidfirst inter-layer insulator; planarizing said second inter-layerinsulator by a chemical and mechanical polishing; and selectivelyetching said second inter-layer insulator to form a second aperturepositioned over said first contact hole.
 2. The method as claimed inclaim 1, further comprising the steps of:selectively forming a secondnon-refractory metal film made of the same metal as said firstnon-refractory metal film within said second aperture; and forming athird inter-layer insulator both on said second inter-layer insulatorand on said second non-refractory metal film within said secondaperture.